1. Field of the Invention
This invention relates to photographic cameras, and more particularly to a single lens reflex camera having an automatic diapharagm control with an electrically operating diaphragm scanning mechanism. Still more particularly, it relates to an improvement of the diaphragm scanning mechanism by the provision of a release device for permitting manipulation of the diaphragm ring while the camera remains in the run down position.
2. Description of the Prior Art
In general, single lens reflex cameras are provided with either or both of two types of automatic exposure control, one of which is to effect automatic adjustment of the diaphragm by an automatic control mechanism in accordance with a preselected shutter speed, and another type, which is to effect automatic determination of an exposure time interval by a delay circuit in accordance with a preselected diaphragm aperture value on the diaphragm presetting ring provided in the lens tube of the camera.
Most of the conventional single lens reflex cameras having shutter preselection and diaphragm preselection automatic exposure control ranges have thus far used exposure meter systems in which, with the diaphragm ring manually set in "Auto" position, the position of the deflected pointer of the exposure meter is scanned, and the scanning result is introduced into the lens aperture mechanism of the camera. In accordance with known techniques, it is possible to record a certain depth of field with this type of camera allowed to remain in the run down position.
In a known camera having an electrically operated diaphragm scanning mechanism by which the diaphragm is automatically formed, a scanning member associated with a variable resistor is driven for scanning operation with movement of the diaphragm presetting ring until the output of the variable resistor reaches a level dependent upon the output of an exposure value computing circuit upon release of the camera. The computed aperture value, thereby the scanning member is held from further movement by electromagnetically operated arresting means. With the camera employing such a new diaphragm scanning mechanism, however, it is impossible to manipulate the diaphragm ring with the camera left in the run down position since the scanning mechanism is interlocked by the stationary arresting means in the arrested position to prevent the diaphragm presetting ring from moving to the initial position. Thus, the diaphragm ring can not be moved throughout the entire aperture value selecting range available when the camera is in the cocked position. After the shutter is closed the photographer must therefore operate the film winding-up or shutter cocking lever. Otherwise, it would be impossible to select a desired aperture value on the diaphragm ring for purposes of predeterminating the utilizable zone of sharpness, or of making the camera ready for a subsequent exposure in either the diaphragm preselection automatic exposure range or the manual exposure range. Since checking the range of sharpness as well as manually setting the diaphragm aperture value on the diaphragm presetting ring can only be done with the camera reset in the cocked position, this manipulation is rather complicated and very difficult for the photographer to master in such a new type of camera.